In recent years, three-dimensional (3D) display technology has become a development trend in the display technology field. The basic principle of parallax-type 3D display technology is that: left and right eyes of a human receive different images with parallax (for example, the left eye and right eye of the human respectively receive a left-eye image and a right-eye image, and parallax is exist between the left-eye image and the right-eye image), and the different images with parallax are subjected to superposition via a brain to form 3D vision. The 3D display device mainly includes a glasses type and a glasses-free type. Because no glasses are required to wear, glasses-free type 3D display devices are attracting an increasing amount of attention. Because there is a limited number of 3D display videos/images currently, besides 3D display function, superior two-dimensional (2D) display function is also desired to be realized in the glasses-free type 3D display devices.